1. Field of the Invention
This application discloses a process for epoxidizing allyl alcohol with peracetic acid in an essentially anhydrous, inert, organic solvent, and hydrolyzing the epoxidized reaction product, glycidol, to form glycerol. When desired, the hydrolysis step can be omitted and glycidol can be recovered as product.
2. Description of the Prior Art
Glycerol is manufactured from allyl alcohol by two principal processes: chlorohydrination followed by hydrolysis of the intermediate "glycerol chlorohydrin," and by hydroxylation with hydrogen peroxide. Both processes involve difficulties in refining the glycerol to obtain a product of marketable quality. U.S. Pat. No. 2,960,447, for example, discloses a detailed procedure involving multiple distillations at controlled pH as a way to purify glycerol derived from allyl alcohol hydroxylation.
Epoxidations of unsaturated organic compounds by organic peracids are generally conducted with one reactant present in a substantial excess in order to obtain acceptable reaction rates and efficiencies. Epoxidation of low molecular weight unsaturated organic compounds, such as allyl alcohol, with organic peracids produces undesirable by-products because of reaction of the epoxide in the presence of the carboxylic acid co-products.
A method of avoiding these difficulties is suggested by British Pat. No. 837,464 which reacts allyl alcohol and hydrogen peroxide in an aqueous solution, the pH of which is controlled by a minor concentration of an inorganic or organic alkaline-reacting substance. This patent suggests using organic compounds, notably amines, which impart to an aqueous solution an alkaline pH, as the preferred means for accomplishing this end. The reaction of the peroxide with allyl alcohol produces glycidol in a dilute aqueous reaction medium containing catalyst and the added amine; although the glycidol can be converted to glycerol by heating such a mixture, isolation of pure glycidol becomes a difficult problem. This British specification discusses the art-recognized problem of epoxidizing unsaturated compounds with organic peracids, that is, that considerable by-product formation occurs with a diminished yield of epoxide.
German Pat. No. 1,081,462, describes epoxidation of high molecular weight unsaturated materials with percarboxylic acids in a diluent (using reduced temperature and pressure to distill acetic acid and volatile materials away from the reaction mixture.) The process operates under conditions such that acetic acid and volatile materials are continuously distilled away from the mixture. This process is not suitable for the epoxidation of allyl alcohol as allyl alcohol is more volatile than either peracetic or acetic acids and is therefore removed from the reaction zone before any substantial conversion to glycidol occurs.